Lecture Notes on the Nervous System

Overview

• Nervous system is the master control and communication system of the body.
• Cells communicate via electrical signals (action potentials) and chemical signals (neurotransmitters).
• Controls homeostasis, movement, sleep/wake cycles, hunger, endocrine system.

Main Functions of the Nervous System

1. Sensory Input

   • Gathers information from internal and external environments.
   • Necessary for deciding actions.

2. Integration

   • Analyzes and interprets sensory input.
   • Determines if a response is needed.

3. Motor Output

   • Executes response to stimuli.
   • Example: A soccer player sees a ball and decides to kick it.

Divisions of the Nervous System

Structural Divisions

• Central Nervous System (CNS)

  • Composed of the brain and spinal cord.

• Peripheral Nervous System (PNS)

  • Composed of nerves that connect the body to the CNS.

Functional Divisions

• Central Nervous System

  • Site of integration for sensory information and motor response planning.

• Peripheral Nervous System

  • Conducts sensory (afferent) and motor (efferent) functions.

Peripheral Nervous System Subdivisions

• Sensory (Afferent) Division

  • Carries sensory stimuli to the CNS.
  • Subdivided into:
    • Somatic Sensory Division: From muscles, bones, skin.
    • Visceral Sensory Division: From organs (abdominal, pelvic, thoracic cavities).

• Motor (Efferent) Division

  • Carries motor responses from CNS to effectors.
  • Subdivided into:
    • Somatic Motor Division: Controls skeletal muscles (voluntary).
    • Autonomic Nervous System: Controls smooth muscles, cardiac muscles, glands (involuntary).
      • Further divided into the parasympathetic and sympathetic divisions.

Histology of Nervous Tissue

• Consists of many cells with little extracellular space.
• Two main cell types:
  • Neurons: Structural and functional units.
  • Neuroglia: Supportive cells.
    • Types in CNS: Astrocytes, Microglial cells, Ependymal cells, Oligodendrocytes.
    • Types in PNS: Schwann cells, Satellite cells.

Astrocytes

• Most abundant and versatile neuroglia.
• Functions:
  • Anchor neurons and blood vessels.
  • Regulate environment, clean up excess neurotransmitters and ions.
  • Form the blood-brain barrier.
  • Repair damaged tissue (forms scar tissue).

Microglial Cells

• Act as phagocytes to clean up debris and pathogens.

Ependymal Cells

• Ciliated cells that circulate cerebrospinal fluid (CSF).

Oligodendrocytes

• Form myelin sheath in CNS to speed up signal transmission.

Schwann Cells

• Form myelin sheath in PNS.

Satellite Cells

• Surround cell bodies in PNS, functionally similar to astrocytes.

Structure of Neurons

• Cell Body: Metabolically active, contains nucleus, endoplasmic reticulum, etc.
• Dendrites: Short, branched processes that receive input.
• Axon: Long process that conducts action potentials.
  • Arises from the axon hillock.
  • Ends in axon terminals containing neurotransmitters.

Terminology

• Axolemma: Plasma membrane of the axon.
• Axoplasm: Cytoplasm within the axon.

Conclusion

• Neurons and neuroglia play essential roles in the functioning of the nervous system.
• Understanding the structure and function is crucial for learning how the nervous system influences all aspects of physiology.